The great fish migration has begun

Rising sea temperatures are pushing shoals of fish hundreds of kilometers from their native grounds, with warm-water fish now landing in northern nets

By Robin McKie / The Guardian

The introduction of sustainable management measures would offset some of these impacts, but stocks still face being cut significantly, the group added.

“Both the sea and land environment are changing,” Fernandes said. “The problem is that we know much less about the sea than the land, so it is harder to observe and to intervene.”

Think of the problem as a double whammy, New Jersey-based Rutgers University marine ecologist Malin Pinsky said.

“Fish have already been reduced to low numbers by intense overfishing and that makes them far less able to deal with increasing temperatures or other effects of climate change,” he said.

Pinsky points to the example of the Atlantic cod in the Gulf of Maine.

“It has been badly hit by intense overfishing. Now it appears that warmer waters have been reducing survival even further. The trouble is that the fisheries management in the area did not realize this and allowed fishing to continue there at a too high level,” he said.

Managing fish stocks in a warming world is proving to be a particularly thorny problem, he added.

“Fish management maps have lines drawn on them, but it turns out fish don’t see those lines,” he said.

As waters warm, fish seek cooler waters and head to higher latitudes, a problem that has also been highlighted in the North Sea. There, closure areas have been set up to protect spawning and nursery grounds of plaice, herring and sand eel from intense fishing.

“But if species shift their distribution in response to climate change it is possible such measures will become less effective in the future,” said a study by a group of scientists led by John Pinnegar, of the British government-funded Centre for Environment, Fisheries and Aquaculture Science.

Another example of the problem was highlighted last week by the New York Times, which noted that the center of the US black sea bass population is now found in waters off New Jersey. In the 1990s, it was hundreds of kilometers further south.

Under fishing rules that were laid down then, North Carolina fishermen are still entitled to the largest share of black sea bass catches — which requires them to steam north for 10 hours to reach the black sea bass’ fishing grounds. By contrast, local New England fishermen are allowed to catch a small fraction of the black sea bass now found in their own neighborhood and must throw all excess overboard.

The issue has already reached the status of causing international discord, as is revealed through the example of the humble mackerel.

“Until recently, mackerel in the Atlantic were fished mainly by Britain, Ireland and Norway, and stocks were protected by an EU quota system,” Roberts said. “Then stocks began to head north, most probably because sea temperatures were rising. Eventually, mackerel reached Iceland — at which point Iceland asked to be included in fishing quotas. This request was rejected — so Iceland went ahead and started catching mackerel in any case.”

The result was a drop in mackerel stocks and an international dispute that lasted several years and which has only recently been resolved — although this respite might only be temporary.